This invention relates to a magnetohydrodynamic (MHD) generating system. In more detail the invention relates to an open-cycle coal-fired two-phase liquid metal MHD generating system. The invention also relates to a method of operating an open-cycle coal-fired MHD generating system.
Within the past few years, the development of MHD power generating systems has been accelerating with the effort focused on coal-fired open-cycle plasma MHD systems. Such systems employ an ionized coal combustion gas seeded with K.sub.2 CO.sub.3 as both the thermodynamic and electrodynamic fluid in the MHD generator at temperatures up to 2800 K. and use heat exchangers (radiant boiler) to transfer thermal energy from the MHD working fluid to a steam bottoming plant.
Less effort has been applied to closed-cycle liquid-metal and plasma MHD systems since these systems are at a lower state of development than is the coal-fired open-cycle plasma MHD system and appear to be more expensive and less efficient than open-cycle plasma MHD. A closed-cycle liquid-metal MHD system employs, for example, an inert gas (helium) as the primary (i.e. thermodynamic) working fluid and a liquid metal (sodium or lithium) as the electrodynamic fluid in the MHD generator at temperatures up to about 1260 K.; and a closed-cycle plasma MHD system employs, for instance, argon seeded with cesium in the MHD generator at a top temperature of around 2000 K. Both also require heat exchangers to transfer the thermal energy from the coal combustor to the MHD working fluid(s) in addition to heat exchanger(s) to transfer thermal energy from the MHD working fluid to the steam bottoming plant.
The open-cycle coal-fired plasma MHD system involves relatively-complex high-risk technology, primarily because of the required high temperatures, and several different elements of the system will require substantial development efforts before commercial development is possible.